1. Field of the Invention
The present invention relates to a fluid coupling apparatus, especially for a motor vehicle transmission.
2. Description of the Related Art
The invention is concerned with an apparatus of the same type as that described and shown in the documents U.S. Pat. No. 4,875,562 and WO-A-94/07058.
In these known designs, such a fluid coupling apparatus is of the type comprising a turbine wheel which is coupled to a turbine wheel hub constituting a driven element, for rotation of the latter with the turbine wheel whereby to couple the latter in rotation with an output shaft, together with an impulse wheel which is coupled to a driving element for rotation with the latter, and of the type comprising a lockup clutch which is adapted to act between the driving element and the driven element, and which comprises two coaxial parts which are mounted for movement of one with respect to the other against the action of circumferentially acting springs, the said parts being an input part comprising a piston, and an output part which is extended radially inwardly by a radial plate element for coupling it in rotation with the hub of the turbine wheel.
A locking clutch, usually called a "lock-up" clutch, for the fluid coupling apparatus is interposed operatively between a driving element and a driven element, and includes a torsion damper, a piston which is mounted for axial movement with respect to the driven element, and at least one friction liner which is associated with the piston and which is adapted to be gripped between the piston and a counter-piston.
In the document U.S. Pat. No. 4,875,562, the piston is so configured as to constitute the input part of the torsion damper, and it carries a friction liner which is arranged to come into contact with the transverse wall of the housing of the fluid coupling apparatus, with this wall constituting the counter piston.
The housing is a sealed casing which is filled with oil, and it is arranged to be coupled in rotation to a driving shaft.
The output part of the damper is fixed to the turbine wheel of the fluid coupling apparatus.
The turbine wheel is fixed to a hub which is arranged to be coupled to a driven shaft for rotation of the latter with it.
Thus, the casing constitutes a driving element, while the hub of the turbine constitutes a driven element, and the lock-up clutch is adapted to act between the casing and the turbine wheel so as to form a bridging means between these latter.
In the document U.S. Pat. No. 4,875,562, the torsion damper includes the piston which retains the springs (or resilient members) externally, together with a guide ring, which may be of divided form, which is carried by the piston, and retains the springs on the inside by virtue of retaining lugs.
The input part thus consists of the piston and the guide ring, while the output part comprises an annular damper plate which is fixed to the turbine wheel.
The output damper plate has engagement lugs which penetrate between the circumferencial ends of two consecutive springs so as to act on these latter.
Each of these lugs penetrates radially between two engagement lugs which are associated with the piston and the guide ring, respectively.
In the document WO-A-94/07058, the guide ring and the damper plate have retaining portions for retaining the springs on the outside and on the inside respectively.
In addition, the damper plate and the guide ring have engagement lugs for acting on the circumferencial ends of the springs.
Because of the retaining means it is possible, after the springs have been fitted by snap fitting of the damper plate behind snap-fitting lugs, to create a unitary sub-assembly which cannot be lost, which is capable of being handled and transported, and which comprises the piston and the torsion damper, this sub-assembly being then able to be fitted in position on the turbine hub.
In the designs proposed in the two said documents, the structure of the turbine hub and the ways used for fastening and/or coupling in rotation the turbine wheel and/or the radial connecting plate element of the output part, are of particular complexity, and are expensive to carry out.
In the document U.S. Pat. No. 4,875,562, the hub of the turbine wheel is a heavy machined component which comprises a radially internal portion in the form of a sleeve, in which internal axial splines are machined. The hub includes a radial plate portion that extends radially outwardly, and on which the turbine wheel is fixed by a set of rivets in the vicinity of that portion of it which lies radially towards the inside, while its radially outward portion includes axial lugs which extend towards the torsion damper. The output part of the lock-up clutch is also guided on a machined cylindrical surface of the radially inner part of the hub of the turbine wheel.
In the document WO-A-94/07058, the output part includes a radial plate element for coupling in rotation, which extends radially inwardly towards an internally splined sleeve, at one end of which it is fitted by seaming, while the turbine wheel is fitted by riveting on a middle portion of the connecting plate portion, in the region of that part of the latter that lies radially towards the inside. In another design, the splined sleeve includes a radial connecting plate portion which is made in one piece and machined, with the radial plate element that connects the output part and the turbine wheel for rotation together being fixed by riveting to its radially outer periphery.